Linux User Accounts (SEC 300) - Chromosom3/TechNotes GitHub Wiki

Linux User Accounts & File Permissions

Creating new user:

Command: useradd

Switches:

  • -m : Adds (creates) user's home directory.
  • -d PATH : Specifies the path for the home directory
  • -k PATH : Specifies the skeleton directory.
  • -s PATH : Specifies the shell the user is going to use.

Example: useradd -m -d /home/dylan -k /etc/skel/ -s /bin/bash dylan

Default values are stored in /etc/default/useradd

Creating a new group:

Command: groupadd

Example: groupadd marketing

This creates the group marketing.

Adding a user to a group:

Command: usermod

Switches:

  • -aG : Adds a user to a group

Example: usermod -aG marketing bob

This adds Bob to the marketing group.

Password Information/Policy:

Command: chage USER

Switches:

  • -l : Lists

Example: chage -l dylan

More: /etc/login.defs contains password max days, password min days, and warn age. /etc/default/useradd is the file that is read when a user is added. Video shows changing the shell from sh to bash. Making bash the default shell for new users. If you change #INACTIVE=-1 to INACTIVE=0 the account will no longer be able to login when the password expires. If you change the SKEL value you dont need to specify -k PATH.

/etc/skel/:

Path: /etc/skel/

Description: /etc/skel/ is the folder that contains any files or folders you want set up for users. Contains a minimum set of files (default files). Can add directories such as Downloads, Pictures, etc.)

{} in mkdir:

Description: When using mkdir you can specify multiple folders by using {}. The below command will create a Pictures folder and Documents folder in /etc/skel/
Example: mkdir /etc/skel/{Pictures,Documents}

List Directory:

Command: ls

Switched:

  • -l : List content of a directory.
  • -d : list permissions of the directory.

Example: ls -ld /home/dylan

Changing file/directory owner:

Command: chown

Example: chown bob somefile.txt

This sets Bob as the owner of somefile.txt.

Changing file/directory group:

Command: chgrp

Example: chgrp marketing /marketing/

This sets the marketing group as the owner group for the marketing folder.

Change File/Folder Permissions:

Command: chmod PATH

Description: Changes the permissions for a file or folder. Can either use rwx or numbers for perms. See the table below for numbers.

Examples:

  • chmod 700 /home/dylan : Makes it so the owner has full read, write, and execute. The owner group and others have no permissions.
  • chmod o-rwx /home/dylan : Makes it so other loses all permissions if they have any.
  • chmod g+rwx /home/dylan : Makes it so the owner group can have full permissions.

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